Process for removing asphalt topping from pavement substrate

ABSTRACT

The invention relates to a method of hydraulically separating asphalt topping from pavement substrate, as opposed to mechanically tearing the bond between the two layers of material. This method results in significantly less damage to the pavement substrate, and is accomplished with the use of a high velocity water jet. The method is unlike erosion of a surface by water in that once an initial erosion cut is made, the asphalt topping and the pavement substrate is separated by debonding.

United States Patent 11 1 Anderson 1 Feb. 19, 1974 54] PROCESS FOR REMOVING ASPHALT 3,704,914 12/1972 1 181011 299/14 3,729,137 4/1973 Cobb et a1. 299/17 x TOPPING FROM PAVEMENT SUBSTRATE Philip J. Anderson, Deerfield, 111.

Institute of Gas Technology, Chicago, 111'.

Filed: Apr. 10, 1972 Appl. No.: 242,798

Inventor:

Assignee:

US. Cl .l 299/17, 51/317, 156/268, 3 156/584 Int. Cl. E2lc 37/06 Field of Search; 156/268, 584; 51/317; 299/17, 299/36 References Cited UNITED STATES PATENTS 10/1971 Anderson 299/17 X Primary ExaminerEdward G. Whitby Attorney, Agent, or Firm-Dominik, Knechtel, Godula & Demur [57] ABSTRACT The invention relates to a method of hydraulically separating asphalt topping from pavement substrate, as

opposed to mechanically tearing the bond between the two layers of material. This method results in significantly less damage to the pavement substrate, and is debonding.

7 Claims, N0 Drawings- PROCESS FOR REMOVING ASPHALT TOPPING FROM PAVEMENT SUBSTRATE This invention relates to a low-noise method for removing asphalt topping from pavement substrates.

It is common practice to asphalt top concrete pavement when it becomes cracked to prolong the pavement life, as removing and replacing the concrete pavement is prohibitively expensive. As the asphalt topping itself eventually cracks and deteriorates, an additional layer is usually added.

This method of road or pavement maintenance is not without problems, for each time a layer of asphalt topping is laid, curbs, drains and accesses through the pavement must be raised by the thickness of the new layer. Furthermore, under bridges and the like, where clearance for trucks and other similar vehicles must be maintained, the thickness of the asphalt topping must be restricted. On bridge decks additional asphalt layers cannot be added where the load would exceed design limits.

Accordingly, it is frequently necessary to remove large areas of asphalt topping from pavement substrates such as concrete. Presently, when a large area is to be removed, tractors and the like having ripper blades are used. For smaller areas, either heaterplaners or conventional pneumatic hammers with cutter tools are used. The use of the tractors with ripper blades not only is extremely noisy, but in many cases, the pavement substrate is often damaged by being pulled up in chunks when the asphalt adheres to it. Heater-planers are highly specialized'equipment used, for example, to undercut existing asphalt where patching is to be done, and are usually flame heating devices used to soften the asphalt, with a blade to cut the softened material. Pneumatic hammers, like the tractorripper, produce high noise levels and tend to tear up the pavement substrate.

The method of the present invention involves hydraulic separation of the asphalt topping from the pavement substrate, as opposed to mechanical tearing of the bond between the two layers of material, thus, significantly, less damage results to the pavement substrate. This hydraulic separation is accomplished with the use of a high velocity water jet. Such water jets have been used in the past for cleaning surfaces of foreign matter such as scale, to fracture or break various materials for mining operations and the like. In the former case, the process is one of mechanical erosion of foreign material, and in the latter case, the process is one of impacting with a water jet of sufficient intensity to fragment the material. The present method is unlike erosion of a surface by water in that once an initial erosion cut is made, the asphalt topping and the pavement substrate is separated by debonding. The energy required to erode away a layer of asphalt topping would be much greater than the energy required to erode a cut or slit and debond the asphalt topping on either side of the slit, as fully described below. Also, much less water is required. The energy required also is substantially less than that required to fragment the asphalt topping to remove it, a process which if technically feasible, furthermore might well result in substantial damage to the pavement substrate.

The method of the present invention also is one which permits controllability of both the area of asphalt topping to be removed and the size of the pieces produced. In addition, in comparison to present removal methods, the operation is one of a low noise level.

Accordingly, it is an object of the present invention to provide a low noise method for removing asphalt topping from pavement substrates.

More particularly, it is an object to provide a method for removing asphalt topping from pavement substrates which is of a low noise level and which results in minimal damage to the pavement substrate.

Still another object is to provide such a method which is applicable for removing both large and small areas of asphalt.

A still further object is to provide such a method which relies on the hydraulic separation of the asphalt topping from the pavement substrate, as opposed to mechanical tearing of the bond between the two layers of material.

Still another object is to provide such a method which permits both controllability of the area of asphalt topping to be removed and the size of the pieces produced. 1

Generally, the process by which the asphalt topping is removed is by pressurizing the interface between the asphalt topping and the pavement substrate with a fluid, preferably water, to a value which exceeds the strength of the bond between the two materials. Access to this interface is gained by cutting a slit or kerf in the asphalt topping to the depth of the interface. The fluid spreads out on both sides of the slit, separating the two layers of material, thus debonding the asphalt topping. The debonded asphalt topping then is physically removed, either by prying up the asphalt topping mechanically with a backhoe or similar tool, or by hand, or by some other appropriate means. Accordingly, it can be seen that the method of the invention generally comprises a three-step process, the first step being to delineate the area in which the asphalt topping is to be removed. The second step is to debond the asphalt topping within the delineated area, and then to physically remove the bonded asphalt topping.

More specifically, in the sequence of operations for removing the asphalt topping, it is preferred to first make a perimeter erosion slit or kerf delineating the area within which the asphalt topping is to be removed. Of course, if this area has pre-existing boundaries which would permit the interface between the asphalt topping and the pavement substrate to be pressurized in the above-described fashion, this initial step can be dispensed with. Normally, however, the area is not this sufficiently defined. The cutting of this slit or kerf preferably is by erosion cutting using a high velocity water jet, either in the form of a continuous stream of water or pulses of water at the desired or necessary pressure. A water jet apparatus of the type sold by Exotech lncorporated, Rockville, Maryland, and disclosed, for example, in one or more of the US. Pat. Nos. 3,520,477; 3,521,820 and 3,490,696, or the equivalent thereof, can be used for this operation. This slit or kerf must extend at least to the interface between the asphalt topping and the pavement substrate, otherwise the asphalt topping will not be debonded. While it is only necessary for the slit to extend to the interface, if it extends beyond the interface into the pavement substrate, the debonding action is not diminished to any substantial degree, and only minor damage to the pavement substrate results, the damage being in the form of a slit the width of the water jet to the depth of penetration.

The manner in which the slit or kerf is made in the asphalt topping will vary depending upon its thickness. For example, this slitting can be accomplished by either varying the parameters of the water jet, that is, its pressure and the nozzle diameter, and the traversing rate, or by making one or more passes with the jet in the slit. Each pass made will extend the depth of the cut, although the additional depth of penetration decreases with each successive pass due to increased distance from nozzle to the material.

The asphalt topping within the delineated area next is removed by pressurizing the interface between the asphalt topping and the pavement substrate, using the same high velocity water jet. The water being at a pressure' which exceeds the strength of the bond between the two materials, spreads out on both sides of the slit or kerf, separating the two layers of material. This debonding of the asphalt topping is best accomplished by making parallel slits or kerfs within the perimeter of the area of asphalt topping to be removed. The spacing between these slits or kerfs will vary with the asphalt type and thickness and the parameters of the water jet. The optimum spacing is one for which the debonding from each adjacent cut will just overlap.

Tilting the device which produces the water jet to either side so that the jet impinges at an angle does not effect the width of debonding on either side of the cut. It does increase the depth required for penetration to the interface and, consequently, the energy required in the water jet.

Once the asphalt topping has been debonded, it can be physically removed using any appropriate method such as, for example, by prying the slices mechanically with a backhoe or similar tool, or by hand. Removal is readily accomplished, since the asphalt topping is almost completely debonded from the pavement substrate.

SPECIFIC EXAMPLE nozzle one milli a small percentage of the total area and offered no significant resistance to peeling off the asphalt topping.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and certain changes may be made in carrying out the above method. Accordingly, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

Now that the invention has been described, what is claimed as new and desired to be secured by Letters Patent is:

1. A low noise process for removing asphalt topping from pavement substrate comprising the steps of: forming a slit in the asphalt topping to the depth of the interface between the asphalt topping and the pavement substrate; debonding the asphalt topping on both sides of the slit by pressurizing the interface between the asphalt topping and the pavement substrate with a fluid to a value which exceeds the strength of the bond between the asphalt topping and the pavement substrate so that the fluid spreads out on both sides of the slit formed in the asphalt topping and separates the asphalt topping from the pavement substrate; and removing the debonded asphalt topping from the pavement substrate.

2. The process of claim 1, including forming the slit in the asphalt topping by erosion cutting the asphalt topping with a water jet.

3. The process of claim 1, including the step of delineating an area in which the asphalt topping is to be removed by forming a slit in the asphalt topping by erosion cutting the asphalt topping to the depth of the interface between the asphalt topping and the pavement substrate with a water jet.

4. The process of claim 1, including the steps of forming a plurality of parallel slits in the asphalt topping, and debonding the asphalt topping on both sides of each of the slits.

5. The process of claim 4, including spacing the parallel slits such that the debonding from each adjacent slit will overlap.

6. The process of claim 1, the debonding of the asphalt being accomplished by use of pulses of fluid.

7. The process of claim 1, the debonding of the asphalt being accomplished with a continuous stream of fluid. 

1. A low noise process for removing asphalt topping from pavement substrate comprising the steps of: forming a slit in the asphalt topping to the depth of the interface between the asphalt topping and the pavement substrate; debonding the asphalt topping on both sides of the slit by pressurizing the interface between the asphalt topping and the pavement substrate with a fluid to a value which exceeds the strength of the bond between the asphalt topping and the pavement substrate so that the fluid spreads out on both sides of the slit formed in the asphalt topping and separates the asphalt topping from the pavement substrate; and removing the debonded asphalt topping from the pavement substrate.
 2. The process of claim 1, including forming the slit in the asphalt topping by erosion cutting the asphalt topping with a water jet.
 3. The process of claim 1, including the step of delineating an area in which the asphalt topping is to be removed by forming a slit in the asphalt topping by erosion cutting the asphalt topping to the depth of the interface between the asphalt topping and the pavement substrate with a water jet.
 4. The process of cLaim 1, including the steps of forming a plurality of parallel slits in the asphalt topping, and debonding the asphalt topping on both sides of each of the slits.
 5. The process of claim 4, including spacing the parallel slits such that the debonding from each adjacent slit will overlap.
 6. The process of claim 1, the debonding of the asphalt being accomplished by use of pulses of fluid.
 7. The process of claim 1, the debonding of the asphalt being accomplished with a continuous stream of fluid. 